1. Field of the Invention
The present invention generally relates to deposition of metal film onto a seed layer deposited on a substrate. More particularly, the present invention relates to the structure and operation of electric contact elements used to apply electricity to a substrate during metal film deposition on a seed layer on a substrate.
2. Background of the Related Art
Electroplating is used for the fabrication of lines and to form interconnect features, e.g. vias, trenches, and electric contacts. One embodiment of a feature-filling process including electroplating involves initially depositing a diffusion barrier layer upon the substrate by a process such as physical vapor deposition (PVD), chemical vapor deposition (CVD), or electroless deposition. A seed layer is then deposited over the diffusion barrier layer on the substrate by a process such as PVD, CVD, or electroless deposition. A metal film is electroplated on the seed layer on a substrate. The deposited metal film is planarized by a process such as chemical mechanical polishing (CMP) to define conductive interconnect features. Metal film deposition by electroplating is accomplished by establishing a voltage/current level between the substrate seed layer and an anode.
FIG. 1 shows a cross sectional view of a typical electro-chemical deposition (ECD) system 10. Generally, the ECD system 10 includes a electrolyte cell 12, a substrate holder system 14 disposed above the electrolyte cell 12, an anode 16, and an electric contact ring 152. A plurality of grooves 24 are formed in the lower surface of the substrate holder system 14. A vacuum generator 25 fluidly communicates with the grooves 24 to create a vacuum capable of retaining the substrate 22 to the substrate holder system 14 during processing.
FIG. 2 shows a generally cylindrical electric contact ring 152 that contains a plurality of embedded metal or metal alloy electric contacts elements 56. Each electric contact elements 56 extends radially inwardly from the electric contact ring and physically contacts a part of the conductive seed layer on the substrate 22. The electric contact elements 56 may include electric contact pins, electric contact rods, electric contact surfaces, electric contact pads, or any other known types of electric contact elements. A controller 222 interacts with a power supply to control the application of electric currents/that flow via electrolyte solution contained in the electrolyte cell 12, from the electric contact elements 56 and the seed layer on the substrate and the electric voltage between the anodes and the seed layer.
There are a variety of factors relating to electric contact elements that can affect current density uniformity across the seed layer on the substrate and the uniformity of metal film deposition rate across the substrate seed layer. Because the electric contact ring is exposed to the electrolyte solution, conductive portions of the electric contact ring 152 that contact the electrolyte solution, such as the electric contact elements 56, accumulate metal film deposits during electroplating. The metal film deposits on each electric contact element may form geometrically different electric contact elements 56, and each electric contact/deposit combination may apply a unique current density to the substrate seed layer. Differing current densities powered by the electric contact elements having different electrical properties resulting from their varying geometric form result in a non-uniform current density distribution across the substrate seed layer during plating. Additionally, in inconsistent metal film deposition on the substrate seed layer produces variations in the metal film deposition between different substrates.
Furthermore, the electric current density applied to the plating surface of the substrate tends to decrease as the distance increases from the electric contact elements. The non-uniform current density across the substrate seed layer result in variations of deposition rates across the seed layer. A fringing effect also occurs at the edge of the substrate due to the localized electric field emitted by the electric contact elements where electric contact elements 56 contact the seed layer. The fringing effect causes a higher deposition rate on the seed layers near the edge of the substrate, which also contribute to non-uniform metal film deposition results.
It is difficult to effectively seal between the substrate and the electric contact ring 152 as a result of the shape of the electric contact elements that extends between the substrate and the electric contact ring. Because the electric contact elements 56 only contact a small portion of the substrate seed layer area, a space is created between each pair of adjacent electric contact elements, the electric contact ring 152, and the substrate 22 often allows some electrolyte solution to fluidly flow to the backside of the substrate, and thereby deposit metal films thereon. The metal film deposition on the backside or edge of a substrate that forms as a result of the electrolyte solution flowing to the substrate backside are known as xe2x80x9cbackside depositsxe2x80x9d. The backside deposits may bond the substrate to the electric contact elements 56 during processing. Breaking the backside deposits that adhere the substrate to the electric contact elements require application of force to the substrate that may bend or damage the substrate. Breaking the backside deposits may also cause problem related to broken deposited metal film material. For example, broken deposit particles may become lodged in post-plating handling devices and contaminate subsequent system components. Scattered, broken deposits are also a source of contamination and potential damage to the substrate. The fragmented metal film deposits may generate particles that contaminate and limit the effectiveness of metal film deposition within the electrolyte solution.
Therefore, there remains a need for an ECD system in which the electric contact elements are effectively isolated from the electrolyte solution such that the formation of metal film deposits on the electric contact elements is limited. Such electric contact elements would enhance the uniformity of the electrical current density across the substrate seed layer in an electrolyte cell, and therefore facilitate a uniform deposition thickness of the metal film across the seed layer on the substrate. The electric contact elements should be positioned to allow for effective sealing against the flow of electrolyte solution around the side and backside of the substrate.